1. Field of the Invention
This invention relates to regenerative combustion devices. More particularly, the present invention relates to a regenerative combustion device which produces a sound source or concussion for seismic surveying, well stimulation, or other purposes.
2. State of the Art
Subsurface exploration, such as for water, oil and gas, or other desired subsurface substances frequently requires the use of subsurface seismic sources. For example, when performing a subsurface survey of a particular region, the surveyor may drill an exploratory well to a desired depth, then lower an explosive charge into the hole on a tether. A plurality of detection stations are placed upon the ground in the area surrounding the exploratory well, and the explosive charge is then detonated. The characteristics of the sound emanating from the explosion are detected and recorded at each detection station. This process provides information which allows the creation of a subsurface profile of the characteristics of the rock strata in the region around the exploratory well.
However, to obtain useful information, it is necessary to repeat this process many times with explosives at different depths, and detection stations in different positions. Accordingly, it is necessary to repeatedly lower new charges into the exploratory well, which may be hundreds or thousands of feet deep. This is a slow process, which significantly impedes the progress of subsurface seismic surveying, and is also expensive because the explosive charges are destroyed with each detonation.
Similarly, concussion devices are also sometimes used to stimulate production in a subsurface well by fracturing the rock strata at certain locations in the well. As with seismic surveying, this procedure is also currently done using explosives, which must be lowered into the well. However, because an oil-bearing formation, for example, may extend for a significant depth, the process is preferably performed several times at varying depths and in multiple wells. Consequently, the same problem of having to repeatedly raise and lower a charge into a well affects this type of operation.
It would therefore be desirable to have a seismic sound source which is regenerative and can repeatedly produce a sonic pulse without having to be removed from its position, and does not require the addition of chemicals for each ignition.
To address some of the above and other needs, the present invention comprises a regenerative combustion device, such as a sealed vessel, having a combustion zone, and chemicals contained within the combustion zone having a first equilibrium state, and a second combustible state, and means for transforming the chemicals from the first equilibrium state to the second combustible state, such as electrodes. An igniter, such as a spark plug or similar device, is disposed within the combustion zone for igniting combustion of the chemicals in the second combustible state. Advantageously, the combustion products are entirely contained within the combustion zone, and the chemicals are selected such that the combustion products naturally chemically decay into the chemicals in the first equilibrium state over time following combustion. The combustion device may thus be repeatedly reused, requiring only a brief wait after each ignition to allow the combustion products to precipitate or regenerate back to the first equilibrium state.
In an alternative embodiment, the combustion zone may be formed by means of packers which are disposed above and below a region of a well, such that the sides of the well are directly exposed to the combustion. This promotes fracture of the rock strata of the sides of the well so as to stimulate liquids flowing from the pores in the rock layer.
In yet another alternative embodiment, the sealed device may be entirely buried, such that ignition may be caused at will over long or unpredictable intervals at the precise location of the device. The device may also be used in water as a seismic source for underwater surveying, etc.